Primarily in interventions in which the doctor inserts medical instruments such as catheters into body channels, taking serial exposures by means of X-ray image technology plays a major role. During such an intervention a C-arm device is generally used to continuously take X-ray fluoroscopy images of the affected area of the body and these are displayed on a monitor. The doctor uses this display, in which the inserted instrument is identifiable in the corresponding environment, to navigate the instrument, in particular a guide wire or a catheter inside a blood vessel. The fluoro scopic X-ray images are taken with as small a dose of X-rays and as low an image acquisition frequency as possible, in order to minimize the patient's exposure to X-ray radiation. However, the small dose of X-rays means there is a very low signal-to-noise ratio, which severely limits the quality of the image. In particular, the background of the image frequently stands out because of undesired noise. The low image display frequency, which corresponds to the image acquisition frequency of generally only 7.5 or 15 Hz, has the additional consequence that the background noise appears as extremely coarse-grained.
U.S. Pat. No. 4,771,342 discloses a method for adjusting the quality of images from a video source to the quality of images acquired by means of an emulsion film, which includes a change in the image regeneration rate and the contrast ratio as well as a gamma correction.
European patent EP 0 674 426 B1 discloses a method for generating a digital semitone display of an original image, the display comprising a field of values of an output cell, representing the color content of pixels of the original image, and comprising the determination of cell values for consecutive output cells, for which cell values have not previously been determined. Also provided is a noise generator for the addition of a generated noise.
Unexamined application WO 2004/047021 A1 discloses a method for converting a first image into a second image, the second image having a higher image resolution after conversion than the first image, and noise being added to the second image.